Technical Field
The present invention relates to an optical pressure-sensitive adhesive sheet.
Background Art
Recently, display devices such as liquid crystal displays (LCDs) or input devices, such as a touch panel, which is used by combining the display device has been widely used in various fields. In manufacturing the display devices or the input devices, a pressure-sensitive adhesive sheet is used for laminating optical members (see, for example, Patent Document 1).
A touch panel has been considered as a trend of an image display method, and in particular, an electric capacity type touch panel has been widely used. The electric capacity type touch panel has a configuration in which many members are laminated, and a pressure-sensitive adhesive sheet is used for the purpose of laminating the members. An example of the electric capacity type touch panel may include an electric capacity type touch panel having a laminated structure of cover glass/pressure-sensitive adhesive sheet/conductive film such as an indium tin oxide film (ITO film)/glass substrate.
The electric capacity type touch panel has a structure in which, when the touch panel is touched by a finger, the capacitance of the corresponding position is changed, and detection (sensing) is performed when the amount of the capacitance changed exceeds a predetermined critical value. In the touch panel having a laminated structure of cover glass/pressure-sensitive adhesive sheet/conductive film (ITO film)/glass substrate, the capacitance changed by touching the panel with a finger needs to be transmitted to a detection part (sensing part) of the touch panel (T/P). Accordingly, the pressure-sensitive adhesive sheet used in the electric capacity type touch panel needs to have high relative dielectric constant. Meanwhile, if relative dielectric constant of the pressure-sensitive adhesive sheet is too high, noise tends to be easily detected, and in the case where an output signal is changed, the transmission time of a signal tends to be delayed, thereby causing a problem in detection sensitivity (sensing sensitivity).
The pressure-sensitive adhesive sheet used in the electric capacity type touch panel needs to have an excellent adhesion property to members constituting the touch panel. For example, the pressure-sensitive adhesive sheet used in the electric capacity type touch panel having a laminated structure of cover glass/pressure-sensitive adhesive sheet/conductive film (ITO film)/glass substrate needs to have an excellent adhesion property, particularly, to a cover glass.
Patent Document 1: JP 2002-363523 A